1. Field of the Invention
The present invention concerns an adjustable-height column, especially for chairs, of the type having a selectively blockable pneumatic piston-cylinder unit as a lift unit, in which the spring action of the piston-cylinder unit is bypassed at a desired depth (retraction) setting and is replaced by a mechanical spring element.
2. The Prior Art
German Utility Model G 7,623,283 discloses an adjustable-height column having a selectively blockable piston-cylinder unit as a lift unit. The piston-cylinder unit is a pneumatic spring which can be selectively blocked by means of a tripping device that acts on a blocking valve to maintain a desired height. At the desired height, the piston-cylinder unit has an elastic, or resilient, give under changing loads, which is regarded as comfortable, especially in chairs.
An additional spring, such as a compression spring or an elastomer block, is arranged in series with the pneumatic spring at the base of the column. Its purpose is to prevent the violent striking of the cylinder of the piston-cylinder unit with the bottom of the column, and/or to effectuate a spring action, when the piston rod is in its extreme retracted position.
It has been found that the spring action of the additional spring, in combination with the blocked pneumatic spring, is perceived as being rather uncomfortable, especially because the pneumatic spring exhibits the greatest rate of spring action (increased pushout force) when the piston rod is fully retracted.
The object of the present invention is to eliminate this deficiency in comfort which results from the described prior art.